Method for fractionating a solution

ABSTRACT

The invention relates to a method for fractionating a solution by a chromatographic simulated moving bed method in which the liquid flow is effected in a system comprising at least two sectional beds in different ionic forms. The fractions enriched with different components are recovered during a multi-step sequence including the following operations, i.e., phases: feeding phase, eluting phase, and recycling phase. The liquid present in the sectional packing material beds with its dry solids concentration profile is recycled during the recycling phase in a loop comprising one, two, or more sectional packing material beds. The method can be employed for the following examples, fractionating sulphite cooking liquor, molasses, and vinasse.

The present invention relates to a method for fractionating a solutioninto two or more fractions enriched with different components. Inparticular, the invention relates to a method for fractionating asolution by a chromatographic simulated moving bed method in which theliquid flow is effected in a system comprising at least twochromatographic sectional packing material beds in different ionicforms, in which the dissolved substances present in the solution areseparated from each other, and if the solution to be treated comprisessubstantial amounts of ions, the system also comprises a unit where theion equilibrium of the solution is changed.

Fractionation of a solution comprising many dissolved substances intofractions enriched with different components is often necessary torecover the desired components as pure as necessary. The method of theinvention can be employed to carry out such fractionation. A sulphitecooking liquor, for instance, can be fractionated by the method so as togive a fraction rich in monosaccharides and/or a fraction rich inlignosulphonates; furthermore, molasses or vinasse can be fractionatedin this way to obtain fractions rich in a sugar, such an sucrose, and/orbetaine.

The method of the invention is particularly well suitable for recoveringmonosaccharides from a sulphite cooking liquor, particularly forrecovering xylose from a hardwood sulphite cooking liquor, in acontinuously operated process by which also a fraction enriched withlignosulphonates can be recovered, if desired.

Sulphite cooking liquor in this context denotes liquor employed insulphite cellulose cooking, liquor obtained after such cooking, or apart thereof.

It is known per se to use ion exchange resins of different ionic formsin chromatographic separation methods. Finnish Patent 59 388 describeschromatographic separation of polyols, employing columns packed with acation exchange resin in different ionic forms (resin with a polystyreneskeleton cross-linked with divinylbenzene and activated with sulphonicacid groups). Finnish Patent 69 296 discloses a chromatographic methodfor the fractionation of polyols, in particular to obtain pure xylitol.Also this method employs a resin with a polystyrene skeletoncross-linked with divinylbenzene and activated with sulphonic acidgroups, packed in parallel columns; in some columns, the resin is inearth alkaline form and in the other columns in Al³⁺ or Fe³⁺ form.

U.S. Pat. No. 4,631,129 discloses the separation of sugars andlignosulphonates from a sulphite spent liquor by a process comprisingtwo chromatographic treatments with ion exchange resins in differentionic forms. In the first treatment, the sulphite spent liquor isintroduced into a chromatographic column comprising a strong acid resinused as column packing material in metal salt form; the metal ion ispreferably a metal ion of the spent liquor, usually calcium or sodium. Asubstantially sugarless fraction rich in lignosulphonates and a fractionrich in sugars are obtained from this column by elution. The latterfraction is subjected to a softening treatment, and its pH is adjustedto be in the range 5.5 to 6.5, whereafter it is introduced into thesecond chromatographic column containing resin in monovalent form, and asecond fraction rich in sugars and a second fraction rich inlignosulphonates and salts are obtained therefrom by elution. It isstated in this patent that the process is capable of recovering sugars,e.g. xylose contained in hardwood sulphite spent liquor, in a very highpurity and high yields. However, a drawback of the method is that thedry solids profile which has been formed in the first chromatographictreatment and in which the components are already partly separated isdestroyed in the softening treatment and pH adjustment and thus cannotbe utilized in the second chromatographic treatment. The method is alsocomplicated by the steps of concentration and additional pumping towhich the solution is subjected. All of these factors add to investmentcosts. Furthermore, this method and all prior art chromatographicseparation methods in which ion exchange resins of different ionic formsare used are attended by the drawback that they are typically batchmethods and are not suitable for fractionating solutions on anindustrial scale.

Continuously operated chromatographic separation processes nowadayscommonly employ the simulated moving bed method, which is known inmodifications developed for a variety of different applications.

The simulated moving bed method enables a separating performance as highas several times that of the batch method, and also significantly lowerdilution of the products (consumption of eluent).

The simulated moving bed method may be either continuous or sequential,as described in the copending Finnish patent applications 930321 and932108 (corresponding to international patent applications WO 94/17213and WO 94/26380, respectively). In the continuous simulated moving bedmethod, typically all flows are continuous. These flows are: supply offeed solution and eluent, recycling of liquid mixture, and withdrawal ofproducts. The flow rate for these flows may be adjusted in accordancewith the separation goals (yield, purity, capacity). Normally, 8 to 20sectional packing material beds are combined into a single loop. Thefeed and product withdrawal points are shifted cyclically in thedownstream direction in the packing material bed. On account of thesupply of eluent and feed solution, the withdrawal of products, and theflow through the packing material bed, a dry solids concentrationprofile is formed in the packing material bed. Components having a lowermigration rate in the packing bed are concentrated in the back slope ofthe dry solids concentration profile, and respectively components havinga higher migration rate in the front slope. The points of introductionof the feed solution and eluent and the withdrawal points of the productor products are shifted gradually at substantially the same rate atwhich the dry solids concentration profile moves in the packing materialbed.

The feed and withdrawal points are shifted cyclically by using feed andproduct valves located along the packing material bed typically at theupstream and downstream end of each sectional packing material bed. Ifit is desired to recover product fractions of very high purity, shortcycle times and a plurality of sectional packing material beds must beemployed (the apparatus has the requisite valves and feed and withdrawalequipment).

In the sequential simulated moving bed method, not all flows arecontinuous. In the sequential simulated moving bed method, the flowsare: supply of feed solution and eluent, recycling of liquid mixture,and withdrawal of products (eluting phase; 2 to 4 or more products). Theflow rates and the volumes of the different feeds and product fractionsmay be adjusted in accordance with the separation goals (yield, purity,capacity). The method comprises three basic phases: feeding, elution andrecycling. During the feeding phase, a feed solution, and possibly alsoan eluent during a simultaneous eluting phase, is introduced intopredetermined sectional packing material beds, and simultaneously aproduct fraction or fractions are withdrawn. During the eluting phase,eluent is introduced into a predetermined sectional packing material bedor predetermined sectional packing material beds, and during thesephases two, three or even four product fractions are withdrawn. Duringthe recycling phase, no feed solution or eluent is supplied to thesectional packing material beds and no products are withdrawn.

Sequential simulated moving bed methods are disclosed in Britishpublished application 2 240 053 and U.S. Pat. No. 4,970,002, forinstance. A sequential simulated moving bed method applied to therecovery of betaine and sucrose from beet molasses is disclosed inFinnish Patent 86 416 (U.S. Pat. No. 5,127,957). Also theabove-mentioned copending Finnish patent applications 930321 (filingdate Jan. 26, 1993) and 932108 (filing date May 19, 1993) relate to asequential simulated moving bed method, the first applied to thefractionation of molasses and the latter to the fractionation ofsulphite cooking liquor. As is described in these applications, thesimulated moving bed method may be a multistep process.

The object of the present invention is a chromatographic method for thecontinuous fractionation of solutions, employing ion exchange resins oftwo or more different ionic forms, so that the dry solids concentrationprofile formed upon passage of the solution through the chromatographicpacking material having a first ionic form is passed to thechromatographic packing material having a second ionic form without thepartially separated components being remixed, and/or that theconcentration and pumping stages of the solution, included in the priorart methods for fractionating solutions with packing material of twodifferent ionic forms, can be avoided.

By the method of the invention, valuable components of solutionsproduced as by-products in industry, such as monosaccharides andlignosulphonates from sulphite cooking liquor in the pulping industryand sugar, such as sucrose, and/or betaine from molasses produced in thesugar industry or vinasse produced in the fermentation industry, can beadvantageously recovered. The method of the invention is particularlysuitable for the recovery of xylose from a hardwood sulphite cookingliquor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the separation curves of column 1.

FIG. 2 shows the separation curves of column 2.

FIG. 3 shows the separation curves of column 3 for the removal ofdivalent cations.

FIG. 4 shows the separation curves of column 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a simulated moving bed method in whichthe liquid flow is effected in a system comprising at least twosectional packing material beds of different ionic forms. Betweenfractionation operations performed in packing materials of differentionic forms, the solution may be subjected to an additional treatmentstep. For example, if the solution contains ions, the ion equilibrium ofthe solution is changed to be suitable for fractionation in the packingmaterial having another ionic form. A change in the pH is also a changein the ion equilibrium.

A preferred embodiment of the invention is a sequential simulated movingbed in which the products are recovered during a multi-step sequence.

A sectional packing material bed may comprise one column; it isnevertheless also possible to pack several successive sectional packingmaterial beds in a single column, depending on the column structure. Onthe other hand, several successive columns may be connected to form oneor more loops.

Changing of the ion equilibrium of the solution to be suitable forfractionation with a packing material having another ionic form maycomprise removal of specific ions from the solution by ion exchange orprecipitation, pH adjustment, and/or filtration, for instance. When thefeed solution is sulphite cooking liquor having calcium as the base,this can be exchanged into sodium by ion exchange, or the calcium may beprecipitated for example as calcium sulphite or calcium sulphate with asodium sulphite solution or sulphuric acid. The dry solids profile canbe maintained essentially intact when the precipitation is performed forexample in a tube reactor. The apparatus for carrying out suchtreatments can be connected in series between the sectional packingmaterial beds having different ionic forms.

The ionic form of the packing material in this context means the ionequilibrium; for instance one sectional packing material bed may bepredominantly in the calcium form and partly in the magnesium and/orsodium form. The ionic form of the packing material is equilibratedaccording to the ionic form of the feed solution employed, and/or it isseparately adjusted to suit the solution to be treated in each case.

The ionic form of the sectional packing material beds is selected inaccordance with the solution to be fractionated. When the feed solutionis sulphite cooking liquor, for instance, the packing material bed forthe first fractionation treatment is preferably in the base form of thecooking liquor (often calcium or magnesium) and the packing material bedfor the second fractionation treatment in monovalent metal ion form,e.g. Na⁺ and/or K⁺ form. In the fractionation of vinasse, preferably themonovalent form (e.g. Na⁺ or K⁺) is first used, followed by the divalentform (e.g. Ca²⁺ or Mg²⁺).

The method of the invention may be employed to fractionate sugarsolutions as well. For example from a solution obtained from lactose byalkaline isomerization and containing lactose, lactulose and galactose,a fraction enriched with galactose can be separated with a packingmaterial in Na⁺ form, And fractions enriched with lactulose and lactosecan be separated from one another with packing material in Ca²⁺ form.Likewise, salts can be removed from molasses, or maltose can be removedfrom syrup, with a packing material in K⁺ /Na⁺ form, and aftersubsequent inversion of sucrose, being carried out as an intermediatestep, fractions enriched with glucose and fructose can be separated fromone another with a packing material in Ca²⁺ form.

In a preferred sequential simulated moving bed method of the invention,the product or products are recovered by employing a multi-step sequencecomprising the following operations, i.e. phases: feeding phase of thesolution to be fractionated, eluting phase and recycling phase.

During the feeding phase, the solution to be fractionated (feedsolution) is supplied to the sectional packing material bed, and acorresponding amount of a product fraction is recovered at a pointdownstream in the flow direction, which may be either in the samesectional packing material bed as the feed point (in which case theother sectional packing material beds in the system may be in theeluting or recycling phase, for instance) or in a Sectional packingmaterial bed different than the feed point, and connected in series(possibly through other sectional packing material beds and/or a unitchanging the ion equilibrium) with the sectional packing material bed towhich feed solution is supplied.

During the recycling phase, the liquid present in the sectional packingmaterial beds with dry solids profile is recycled in a loop comprisingone, two or more sectional packing material beds.

In the eluting phase, eluent is introduced into a sectional packingmaterial bed and a corresponding amount of product fraction or fractionsare recovered at a downstream point of the packing material bed, fromthe same or a downstream sectional packing material bed.

A process step comprises one or more of the above simultaneous identicalor different phases. A step can consist of, for example, a feedingphase, recycling phase or eluting phase only, a feeding phase and asimultaneous recycling and/or eluting phase or phases, an eluting phaseand a simultaneous recycling phase or phases, a recycling phase and asimultaneous eluting phase or phases, etc. These steps are repeated oneor several times during the sequence.

These phases are employed to form sequences comprising severalsuccessive process steps. In accordance with the invention, a sequencecomprises 4 to 20, preferably 4 to 10 steps.

A sequence comprising the above steps is repeated about 6 to 8 times toequilibrate the system, whereafter the process is continued in a stateof equilibrium.

Typically 2 to 12, preferably 2 to 7, chromatographic sectional packingmaterial beds grouped into one or more loops are employed in the methodof the invention. A loop may comprise one, two or more sectional packingmaterial beds packed in one or more columns.

In the method of the invention, recycling is employed such that one,two, three or even more discrete successive loops are formed in therecycling phase. For example, when the number of sectional packingmaterial beds is three, these may form one loop or preferably two loops(in which case the method is called a two-phase method), one of theloops comprising one and the other two sectional packing material beds.When the system comprises several successive discrete loops, each ofthese may be closed or open, that is, when the liquid is recycled in oneloop, eluent can be introduced into the other loop and a productfraction can be withdrawn therefrom. During the feed and elution, theflow through the packing material beds may be effected between thesuccessive loops, the flows conveying material from one loop to another.During the recycling phase, the loop is closed and isolated from theother loops. A separate dry solids profile is recycled in each of thediscrete loops. Each sectional packing material bed may form onediscrete loop. On the other hand, a loop may comprise one or moresectional packing material beds.

A particularly preferred embodiment of the invention is a simulatedmoving bed method employing sectional packing material beds in twodifferent ionic forms for simultaneous recovery of xylose andlignosulphonates from a hardwood sulphite cooking liquor on anindustrial scale in high yields and advantageous purity for furtherprocessing or use. Furthermore, the salts, oligosaccharides and othercomponents in the sulphite cooking liquor which are harmful to theproduction of pure crystalline xylose, for instance, can beadvantageously removed from the xylose fraction by this method. If asoftwood sulphite cooking liquor is employed as the raw material, theprevailing monosaccharide is mannose and a mannose-rich fraction isobtained by the method.

If in the method only a monosaccharide (e.g. xylose) fraction and aresidue fraction are separated from the sulphite cooking liquor, thelignosulphonates are eluted with organic and inorganic salts into theresidue fraction. However, the method of the invention yields a drysolids profile in which lignosulphonates are concentrated in relation tosalts at the front slope of the dry solids profile, and they can berecovered by suitably selecting the product withdrawal point.

The implementation of the method (e.g. the ionic forms of the sectionalpacking materials; number of loops to be formed) and the processparameters are chosen for example in accordance with the composition ofthe feed solution employed as the raw material so as to yield an optimumresult with regard to product purity and yield and the separationcapacity of the packing material.

Preferably a strong acid gel-type cation exchange resin (e.g. "Finex","Amberlite" or "Dowex") is employed as the packing material, and in thefirst chromatographic fractionation treatment it preferably has theionic form of the feed solution. Prior to separation, the solids presentin the solution are removed therefrom by filtration.

If the solution to be fractionated is e.g. a sulphite cooking liquor,vinasse or molasses, it is heated to 40° to 100° C., preferably 50° to85° C., prior to being fed into the separation process. In such a case,the eluent employed can be water or a solution obtained fromconcentration of dilute fractions (e.g. condensate obtained fromevaporative concentration) at a temperature 40° to 100° C., preferably50° to 85° C. The linear flow rate of the liquid in the columns is 0.5to 12 m/h, even 20 m/h, preferably 2 to 10 m/h.

The following examples illustrate the invention in greater detail. Theseexamples are not to be construed as limiting the field of the invention,but they are only illustrative of the special embodiments of theinvention.

The dry solids contents indicated have been determined by the KarlFischer method, unless otherwise indicated.

EXAMPLE 1

Two-phase separation method for sulphite cooking liquor

A chromatographic separation apparatus comprising four columns connectedin series was employed. Three of these were separation columns and onewas a column removing divalent cations. The apparatus further compriseda feed pump, recycle pumps, an eluent water pump, flow and pressureregulators, and inlet and product valves for the process streams.Columns 1, 2 and 4 were separation columns and column 3 a column forremoving divalent cations. The two first columns comprised foursectional packing material beds (8 m), the column for removing divalentcations comprised one sectional packing material bed (1.5 m), and thefourth column comprised two sectional packing material beds (4 m).

Each of the four columns was packed with a strong acid cation exchangeresin (Finex V09 C™). The resin had a polystyrene skeleton; it wascross-linked with divinylbenzene and activated with sulphonic acidgroups, and had a mean bead size (in Na⁺ form) of 0.39 mm. The resin hada DVB content of 5.5%. The resin of the first two columns had beenregenerated into Ca²⁺ form and the sectional packing material of columns3 and 4 into Na⁺ form prior to the test.

Test conditions:

Diameter of columns 0.11 m

Height of resin bed in the column for removing divalent cations 1.5m

Total height of resin bed in separation columns 12 m

Temperature 75° C.

Volume flow rate 14-75 l/h

The feed solution was hardwood sulphite cooking liquor whose compositionwas analyzed by HPLC. The cooking liquor was in calcium base form. Theanalysis results are shown in Table 1, where the percentages of thedifferent components are given as per cent by weight on dry solidsbasis.

                  TABLE 1                                                         ______________________________________                                        Analysis of feed solution                                                     ______________________________________                                        Lignosulphonates, %                                                                              42.0                                                       Glucose, %         1.1                                                        Xylose, %          26.6                                                       Galactose + rhamnose, %                                                                          2.0                                                        Arabinose, %       0.6                                                        Mannose, %         1.3                                                        Total monosaccharides, %                                                                         31.6                                                       Oligosaccharides, %                                                                              1.0                                                        Others, %          25.4                                                       pH                 3.1                                                        Conductivity, mS/cm                                                                              6.7                                                        Colour, ICUMSA     84000                                                      Dry solids content, % by wt.                                                                     49.3-53.9                                                  ______________________________________                                    

Fractionation was performed by a four-step sequence. The sequence had acycle length of 92 minutes, and it comprised the following steps:

Step 1: 17 l of feed solution was introduced (feeding phase) into column1 at a volume flow rate 33 l/h, and 17 l of residue (residue 1) waseluted from the downstream end of the same column at the same volumeflow rate. Simultaneously 25 l of eluent water was supplied (elutingphase) to column 2 at a volume flow rate 45 l/h, and 25 l of residue(residue 4) was withdrawn from column 4 at a volume flow rate 45 l/h. Inthis eluting phase, the column for removing divalent cations wasconnected to this open elution loop. The volume flow rate in the columnfor removing divalent cations during the elution was 45 l/h, and thefeed volume from this column was 25 l. Subsequent to the column forremoving divalent cations, the pH of the solution was adjusted to bewithin the range 5.5 to 6.5. After pH adjustment, the solution wasfiltered. The feed from the column for removing divalent cations wasintroduced into the upper portion of the fourth column.

Step 2: Recycling (recycling phase) in the loop formed by columns 1 and2 (13.0 l; 50 l/h) with simultaneous supply of 4.5 l of water to column4 (eluting phase) at a volume flow rate 35 l/h, and elution of a recyclefraction from column 4 (4.5 l; 35 l/h).

Step 3: 20 l of water was introduced into the upper portion of column 1at a volume flow rate 75 l/h, and a residue was eluted (residue 2) fromthe bottom of column 2 (20 l; 75 l/h). Simultaneously 21.5 l of waterwas supplied to the upper portion of column 4 at a volume flow rate 35l/h and a xylose fraction was eluted from column 4 (21.5 l; 35 l/h).

Step 4: Recycling (recycling phase) in the loop formed by columns 1 and2 (4.8 l; 75 l/h) and in the separate loop formed by column 4 (4.2 l; 14l/h).

After the sequence was carried to completion, the process controlprogram was continued and it returned to the beginning, starting thesequence anew from step 1. By repeating this sequence six to eight timesthe system was equilibrated. The method was proceeded with in a state ofequilibrium, and the progress of the separation process was monitoredwith a density meter, a meter for optical activity,. and a conductivitymeter, and the separation was controlled by a microprocessor whichcontrolled precisely the volume flow rates and volumes of feeds,employing quantity/volume measuring devices, temperature controllers,valves and pumps.

In this method, four product fractions were fractionated: a xylosefraction from column 4, one residue fraction from column 1, one residuefraction from column 2 and one residue fraction from column 4. Ananalysis of the product fractions and recycle fraction obtained duringone sequence in a state of equilibrium is shown in Table 2, where thepercentages of the different components are given as per cent by weighton dry solids basis.

The xylose yield from this fractionation was 90.9% calculated from theproduct fractions.

                  TABLE 2                                                         ______________________________________                                        Analysis of product fractions and recycled fraction                                                            Residue                                               Xylose                                                                              Residue 1                                                                              Residue 4                                                                              2     Recycle                                ______________________________________                                        Volume, 1  21.5    17.0     25.0   20.0  4.5                                  Dry solids content,                                                                      17.62   9.25     2.84   20.48 11.29                                K-F, g/100 g                                                                  Xylose, %  65.52   4.33     11.69  2.55  28.16                                Monosaccharides, %                                                                       75.96   5.37     14.38  3.29  35.50                                Oligosaccharides, %                                                                      0.68    0.71     0.39   0.67  1.32                                 Others     23.36   93.92    85.23  96.04 63.18                                ______________________________________                                    

The calcium balance during one sequence in this fractionation in a stateof equilibrium was the following:

In feed solution into column 1: 271 g

Separation from packing material in Ca²⁺ form (columns 1 and 2) intoproduct fractions:

residue 1 60.3 g (3.7% d.s.)

residue 2 150.3 g (3.4% d.s.)

Into column for removal of divalent cations (column 3): 60.4 g

Into packing material in Na⁺ form (column 4): 196 mg Separation frompacking material in Na⁺ form into product fractions:

residue 4 100 mg

xylose fraction 77 mg

recycle 19 mg

EXAMPLE 2

Two-phase separation method for sulphite cooking liquor

Fractionation was performed employing the chromatographic separationapparatus described in Example 1, which comprised two loops, removal ofdivalent cations, and pH adjustment. The sequence carried out differedfrom the procedure of Example 1 in regard to step 2, in which a residuefraction and a recycle fraction were successively eluted with water fromcolumn 4. In this sequence, a fraction rich in lignosulphonates wasadditionally eluted. The volume parameters and volume flow rates of thefeeds and recovered fractions were modified. These modifications weredue to the fact that a different packing material (Relite C-360) wasemployed in the column for removal of divalent cations, and thesectional packing material bed in column 4 had a greater height. Theresin Relite C-360™ had a polystyrene skeleton cross-linked withdivinylbenzene, and it was activated with sulphonic acid groups; thebead size was 0.3 to 1.2 mm and the DVB content 16%. The sectionalpacking material in the other columns was the same as in Example 1. Thefeed solution was the same as above.

Test conditions:

Diameter of columns 0.11 m

Height of resin bed in the column for removing divalent cations 1.5 m

Total height of resin bed in separation columns 13 m

Temperature 75° C.

Volume flow rate 22-50 l/h

A lignosulphonate-rich fraction was eluted from column 2.

Fractionation was performed by a four-step sequence. The sequence had alength of 98 minutes, and it comprised the following steps:

Step 1: 20 l of feed solution was introduced (feeding phase) into column1 at a volume flow rate 22 l/h, and a 20 l residue fraction (residue 1)was eluted from the downstream end of the same column. Simultaneously 33l of water was supplied (eluting phase) to column 2 at a volume flowrate 40 l/h and a residue fraction (residue 4/1, 33 l; 40 l/h) waseluted from column 4.

Step 2: Recycling (recycling phase) in the loop formed by columns 1 and2 (11 l; 35 l/h). Simultaneously 8 l of water was supplied to column 4,and 4 l of residue fraction (residue 4/2) was first eluted from column 4at a volume flow rate of 35 l/h and thereafter 4 l of recycle fractionwas eluted from column 4 at the same volume flow rate.

Step 3: 16 l of water was introduced into the upper portion of column 1at a volume flow rate 45 l/h, and a lignosulphonate-rich fraction waseluted from the bottom of column 2 (16 l; 45 l/h). Simultaneously 22 lof water was supplied to the upper portion of column 4 at a volume flowrate 40 l/h, and a xylose fraction was eluted from column 4 (22 l; 40l/h).

Step 4: Similar to step 4 in Example 1 (recycling in the loop formed bycolumns 1 and 2 4.8 l, 75 l/h; in the loop formed by column 4 0 l; 0l/h).

This sequence was repeated six to eight times, whereafter the system wasequilibrated, and the method was proceeded with in a state ofequilibrium until the column for the removal of divalent cationsrequired regeneration.

An analysis of the product fractions and recycle fraction obtained inthis fractionation during one sequence in a state of equilibrium isshown in Table 3. The percentages of the components are calculated asper cent by weight on dry solids basis.

The xylose yield from this fractionation was 94.7%.

FIG. 1 shows the separation curves of column 1, FIG. 2 the separationcurves of column 2, FIG. 3 the separation curves of column 3 for theremoval of divalent cations, and FIG. 4 the separation curves of column4 for this fractionation.

The lignosulphonate content has been determined by means of UVabsorbance measurement (absorptivity 14.25 l·g⁻¹ ·cm⁻¹).

                                      TABLE 3                                     __________________________________________________________________________    Analysis of product fractions                                                                                  Lignosul-                                                        Residue 4/1  phonate                                                Xylose                                                                             Residue 1                                                                          + recycle                                                                            Residue 4/2                                                                         fraction                                     __________________________________________________________________________    Volume, 1 22.0 20.0 37.0   4.0   16                                           Dry solids content,                                                           K-F, g/100 g                                                                            16.44                                                                              10.07                                                                              4.87   10.61 20.40                                        Xylose, % 70.83                                                                              0.64 7.07   24.01 0.29                                         Monosaccharides, %                                                                      81.86                                                                              0.89 8.65   26.57 0.29                                         Oligosaccharides, %                                                                     1.51 0.00 1.29   5.37  0.00                                         Lignosulphonates, %                                                                     5.02 57.70                                                                              25.60  16.56 65.00                                        Others    11.61                                                                              41.41                                                                              64.46  49.50 34.71                                        __________________________________________________________________________

EXAMPLE 3

Two-phase separation method for sulphite cooking liquor

Fractionation was performed with a chromatographic separation apparatuscomprising four columns. The first loop comprised columns 1 and 2(packing material in Ca²⁺ form), column 3 was a column for the removalof divalent cations in the solution, and a pH adjustment unit wasconnected between column 3 and column 4. Column 4 constituted the latterloop, and its packing material was in the Na⁺ form. The feed solutionand the sectional packing material for the columns were the same as inExample 2.

Test conditions:

Diameter of columns 0.11 m

Height of resin bed in the column for removing divalent cations 1.5 m

Total height of resin bed in separation columns 13 m

Temperature 75° C.

Volume flow rate 22-50 l/h

Fractionation was performed by a five-step sequence. The sequence had alength of 100 minutes, and it comprised the following steps:

Step 1: 20 l of feed solution was introduced (feeding phase) into column1 at a volume flow rate 22 l/h, and a 20 l residue fraction (residue 1)was eluted from the downstream end of the same column. Simultaneously 34l of water was supplied (eluting phase) to column 2 at a volume flowrate 40 l/h, and a residue (residue 4) was eluted from column 4 (34 l;40 l/h).

Step 2: Recycling (recycling phase) in the loop formed by columns 1 and2 (11 l; 35 l/h). Simultaneous recycling (recycling phase) of 3 l at avolume flow rate 40 l/h in the loop formed by column 4.

Step 3: 16 l of water was introduced into column 1 at a volume flow rate45 l/h, and a residue was eluted from column 2 (residue 2, 16 l; 45l/h). At the same time, 4 l of water was supplied to column 4 at avolume flow rate 40 l/h, simultaneously eluting a recycle fraction fromthe bottom of column 4 (4 l; 40 l/h).

Step 4: Recycling (recycling phase) in the loop formed by columns 1 and2 (3.5 l; 50 l/h). 18 l of water was supplied to column 4 at a volumeflow rate 40 l/h, and 18 l of xylose fraction was eluted from column 4at a volume flow rate 40 l/h.

Step 5: Further recycling (recycling phase continued) in the loop formedby columns 1 and 2 (3.5 l; 50 l/h). Simultaneous recycling (recyclingphase) in the loop formed by column 4 (4 l; 30 l/h). During this step,the two recycling phases were synchronized to end at the same time.

This sequence was repeated six to eight times, whereafter the system wasequilibrated, and the method was proceeded with in a state ofequilibrium until the column for the removal of divalent cationsrequired regeneration.

An analysis of the product fractions and recycle fraction obtained inthis fractionation during one sequence in a state of equilibrium isshown in Table 4. The percentages of the components are calculated aspercent by weight on dry solids basis.

The xylose yield from this fractionation was 92.7%.

                  TABLE 4                                                         ______________________________________                                        Analysis of product fractions and recycled fraction                                                            Residue                                               Xylose                                                                              Residue 1                                                                              Residue 4                                                                              2     Recycle                                ______________________________________                                        Volume, 1  18.0    20.0     34.0   16.00 4.0                                  Dry solids content,                                                                      19.25   10.51    5.71   19.94 14.08                                K-F, g/100 g                                                                  Xylose, %  71.08   2.61     6.91   0.48  48.36                                Monosaccharides, %                                                                       83.16   2.87     9.42   0.48  62.02                                Oligosaccharides, %                                                                      0.92    0.43     0.90   0.36  3.18                                 Others     15.92   96.70    89.68  99.16 34.80                                ______________________________________                                    

The fractionation described above was performed also in a variant wherethe divalent ions were removed, instead of ion exchange, byprecipitating the calcium in a tube reactor, as described hereinbelow.

A. Precipitation of calcium as calcium sulphite

The pH of the solution obtained from column 2 and introduced into column3 was adjusted with sodium hydroxide to about 7 at about 60° C. Aquantity of an aqueous solution of sodium sulphite (about 1 M) was addedsuch that the amount of added sulphite ions was about 1.3 times themolar amount of calcium to be precipitated. Kenite 300 diatomaceousearth was employed as an aid in the filtration. Thus it was possible toremove about 90% of the calcium present in the solution. Xylose lossesin the calcium removal thus performed were negligible.

B. Precipitation of calcium as calcium sulphate

The procedure was similar to that of variant A above, but theprecipitation was carried out by adding an amount of sulphuric acid inwhich the number of sulphate equivalents was about 1.5 times that ofcalcium equivalents, and the pH of the solution was adjusted to be inthe range 5.5 to 6 with sodium hydroxide. In this way, it was possibleto remove about 70% of the calcium.

EXAMPLE 4

Three-stage separation method for vinasse

A pilot plant scale chromatographic test apparatus was used. Theapparatus comprised three chromatographic separation columns connectedin series, a pH adjustment unit, a filtration unit, a feed pump,recycling pumps, an eluent water pump, flow and pressure regulators, andinlet and product valves for the process streams. Each of the threecolumns was packed with a strong acid cation exchanged resin (Finex C13S™). The resin had a polystyrene skeleton, it was cross-linked withdivinylbenzene and activated with sulphonic acid groups and had a meanbead size (in Na⁺ form) of 0.36mm. The resin had a DVB content of 8%.The packing material of columns 1 and 2 was in K⁺ form and column 3 wasin Ca²⁺ form. The pH adjustment unit and filtration unit were connectedbetween columns 2 and 3. The pH was adjusted with Ca(OH)₂. The totalheight of the packing material beds in the two first columns was 10 m,and the height of the packing material bed in the third column was 5 m.

The feed solution was vinasse whose composition is shown. in Table 5.The percentages of the different components are given as per cent byweight on dry solids basis.

                  TABLE 5                                                         ______________________________________                                        Analysis of feed solution                                                     ______________________________________                                        Inositol, %      0.4                                                          Glycerol, %      6.3                                                          Betaine, %       13.8                                                         Trisaccharides, %                                                                              0.4                                                          Disaccharides, % 1.6                                                          Monosaccharides, %                                                                             7.9                                                          Others, %        69.6                                                         ______________________________________                                    

Water was used as eluent.

Fractionation was performed by an eight-step sequence. The sequence hada cycle length of 93 minutes, and it comprised the following steps:

Step 1: 7 l of feed solution was introduced (feeding phase) into column1 at a volume flow rate 90 l/h, and a fraction enriched with betaine (7l; 90 l/h) was eluted from column 2. Simultaneous recycling (recyclingphase) in the loop formed by column 3 (6 l; 75 l/h).

Step 2: Feed was continued (feeding phase) into column 1 (5 l; 90 l/h),and a residue was eluted from the bottom of the same column (5 l; 90l/h). Simultaneously eluent was supplied (eluting phase) to column 2 (6l; 120 l/h), and a fraction enriched with betaine was eluted from thebottom of this column (6 l; 120 l/h). The recycling phase was continuedin the loop formed by column 3 (recycling 4 l; 75 l/h).

Step 3: Feed was continued into column 1 (28 l; 90 l/h), and 28 l ofresidue was eluted from the bottom of the same column at the same volumeflow rate. Columns 2 and 3, together with the pH adjustment andprecipitation unit connected between them, formed an open elution loop;40 l of eluent was supplied to column 2 at a volume flow rate 130 l/h,and a fraction enriched with betaine was withdrawn from column 3 (40 l;130 l/h).

Step 4: Recycling in the loop formed by columns 1 and 2 (55 l; 120 l/h)and simultaneously in the loop formed by column 3 (12 l; 75 l/h).

Step 5: 35 l of eluent was introduced into column 1 at a volume flowrate 120 l/h, and 35 l of residue was eluted from column 2 at the samevolume flow rate. Simultaneously 36 l of eluent was supplied (75 l/h) tocolumn 3 and 36 l of residue was eluted from the bottom of the samecolumn at the same volume flow rate.

Step 6: Recycling in the loop formed by columns 1 and 2 (48 l; 130 l/h).Simultaneously 9 l of eluent was supplied to column 3 at a volume flowrate 75 l/h, and 9 l of a fraction enriched with inositol was elutedfrom the bottom of column 3 (75 l/h).

Step 7: Recycling was continued in the loop formed by columns 1 and 2.Simultaneously 28 l of eluent was supplied to column 3 at a volume flowrate 75 l/h and 28 l of a fraction enriched with glycerol was elutedfrom the bottom of column 3 (75 l/h).

Step 8: Recycling was continued in the loop formed by columns 1 and 2.Simultaneous recycling in the loop formed by column 3 (8 l; 75 l/h).

This sequence was repeated six to eight times, whereafter the system wasequilibrated, and the method was proceeded with in a state ofequilibrium.

The following product fractions were fractionated in this method:betaine fractions from columns 2 and 3, an inositol fraction from column3, a glycerol fraction from column 3, two residue fractions from column1, one residue fraction from column 2 and one residue fraction fromcolumn 3. An analysis of the product fractions (with residue fractionscombined) obtained in a state of equilibrium during one sequence isshown in Table 6, where the percentages of the components are given asper cent by weight on dry solids basis.

                  TABLE 6                                                         ______________________________________                                                   Residue  Inositol  Glycerol                                                                             Betaine                                             fractions                                                                              fraction  fraction                                                                             fraction                                 ______________________________________                                        Inositol, %                                                                              0.1      12.5      1.6    --                                       Glycerol, %                                                                              0.3      --        75.9    0.1                                     Betaine, % 2.8       0.2      0.1    77.6                                     Others, %  96.8     87.3      22.4   22.3                                     ______________________________________                                    

EXAMPLE 5

Two-phase concentration of lactulose

A two-loop apparatus comprising five chromatographic separation columnswas used to separate a solution prepared from lactose as follows: Thelactose was isomerized by the conventional method with alkali into alactulose-containing syrup. The resulting syrup was purified in theconventional manner by ion exchange employing ion exchange resins. Thelactulose content of the resulting syrup was 22% on dry solids basis.

Lactose was crystallized from the ion-exchanged syrup twice, so that thelactulose content of the mother solution obtained was 50% on dry solidsbasis and the contents of lactose and other components (e.g. galactose)30% and 20%, respectively.

The columns were packed with the same ion exchange resin as inExample 1. The packing material of the three first columns was in Ca²⁺form and the packing material of the two last two columns in Na⁺ form.

Fractions enriched with lactose and other components (e.g. galactose)were withdrawn from all three columns having a packing material in Ca²⁺form. The first fraction to be recovered was the lactose fraction, andthe last fraction was the fraction enriched with other components(galactose). The lactulose-containing concentrate with average retentionwas introduced into the packing material having Na⁺ form.

A lactose fraction was withdrawn from both columns having a packingmaterial in Na⁺ form, and a fraction enriched with other components(galactose) was withdrawn from the last column (fifth column in thesystem).

The lactulose fraction obtained had a lactulose content of 85% on drysolids basis and a lactose content of 10% on dry solids basis. Thecombined lactose fractions contained 15% of lactulose on dry solidsbasis and 74.7% of lactose on dry solids basis. The lactulose andlactose contents of the combined by-product fraction (which comprisedmainly galactose) were 22% and 18.8% on dry solids basis, respectively.

EXAMPLE 6

Two-phase separation of maltose, glucose and fructose

A two-loop apparatus comprising five chromatographic separation columnswas used to separate a synthetic maltose-containing syrup containingalso glucose and fructose. The solution contained 20% of maltose, 40% ofglucose and 40% of fructose, all calculated on dry solids basis.

The columns were packed with the same ion exchange resin as inExample 1. The packing material of the first column was in Na⁺ form andthe packing material of the next four columns in Ca²⁺ form. A maltosefraction was withdrawn from the first column, and aglucose-fructose-containing concentrate was introduced into the packingmaterial having Ca²⁺ form.

A glucose fraction and a fructose fraction were withdrawn from the thirdand fifth column having a packing material in Ca²⁺ form (the fructosefraction was eluted more slowly).

The withdrawn maltose fraction contained 90% of maltose on dry solidsbasis and 10% of glucose on dry solids basis.

The combined glucose fractions contained 3% of maltose and 95% ofglucose, and the combined fructose fractions contained 1% of maltose and99% of fructose (all on dry solids basis).

EXAMPLE 7

Two-phase separation of cane molasses

Cane molasses was softened and clarified in the conventional manner byphosphatization treatment and by removing the resulting solids bycentrifugation. After the centrifugation, the solution was subjected tofiltration with diatomaceous earth as an aid.

A two-loop apparatus comprising seven columns was used to separate canemolasses thus pretreated, which contained 30% of non-sugars, 40% ofsucrose, 15% of glucose and 15% of fructose.

The packing material of the first three columns was in Na⁺, K⁺ form (inequilibrium with cations in the molasses), and the packing material ofthe other four columns of the apparatus was in Ca²⁺ form.

A non-sugar fraction was withdrawn from all three columns and a sucrosefraction with average retention was withdrawn from the third column,having a packing material in Na⁺, K⁺ form. Theglucose-fructose-containing concentrate which was the slowest to elutewas introduced into the packing material having Ca²⁺ form.

A glucose fraction and a fructose fraction were withdrawn from the fifthand seventh column having a packing material in Ca²⁺ form.

The combined non-sugar fractions withdrawn contained 85% of non-sugarsand 15% of sucrose; the sucrose fraction obtained contained 10% ofnon-sugars and 85% of sucrose (all on dry solids basis). The glucosefractions obtained contained 96% of glucose and 2% of fructose on drysolids basis; the fructose fractions contained 95.6% of fructose and 2%of glucose.

We claim:
 1. A method for fractionating a solution by a chromatographicseparation method in which the liquid flow is effected in a systemcomprising at least two chromatographic sectional packing material beds,characterized in that the system comprises at least two sectionalpacking material beds in different ionic forms, and the fractionation isperformed by the simulated moving bed method, and the solution is passedfrom a sectional packing material bed to the next sectional packingmaterial bed having a different ionic form in such a way that the drysolids concentration profile present in the solution remainssubstantially intact.
 2. A method as claimed in claim 1, characterizedin that fractions enriched with different components are recoveredduring a multi-step sequence comprising feeding phase, an eluting phaseand a recycling phase, wherein the liquid present in the sectionalpacking material beds with its dry solids concentration profile isrecycled during the recycling phase in a loop comprising one, two ormore sectional packing material beds.
 3. A method as claimed in claim 2,characterized in that the sectional packing material beds in the systemform two or more separate loops each comprising one or more sectionalpacking material beds, all of the sectional packing material beds in oneloop having the same ionic form and the sectional packing material bedsof at least two loops having different ionic forms.
 4. A method asclaimed in any one of claims 1 to 3, characterized in that the systemcomprises a unit in which the ion equilibrium of the solution is changedand which can be connected between sectional packing material bedshaving different ionic forms.
 5. A method as claimed in claim 4,characterized in that the ion equilibrium is changed with an ionexchange material.
 6. A method as claimed in claim 4, characterized inthat the ion equilibrium is changed by precipitation.
 7. A method asclaimed in claim 4, characterized in that the change of the ionequilibrium comprises pH adjustment.
 8. A method as claimed in claims 2,characterized in that a step comprises one or more recycling phasesand/or eluting phase and recovery of a product fraction.
 9. A method asclaimed in claim 2, characterized in that a step comprises two or morerecycling phases.
 10. A method as claimed in claim 2, characterized inthat a step comprises a feeding phase and/or one or more eluting phasesand recovery of a product fraction or fractions.
 11. A method as claimedin claim 1, characterized in that the solution to be fractionated is asulphite cooking liquor.
 12. A method as claimed in claim 11,characterized in that the sulphite cooking liquor is a hardwood sulphitecooking liquor, a cooking liquor obtained after such cooking, or a partthereof.
 13. A method as claimed in claim 12, characterized in that theproduct fractions are a xylose fraction and/or a lignosulphonate-richfraction and/or a residue fraction.
 14. A method as claimed in claim 11,characterized in that oligosaccharides are substantially separated intothe residue fractions.
 15. A method as claimed in claim 11,characterized in that the sectional packing material beds in the firstloop in a process step are essentially in divalent cation form and thesectional packing material beds in the last loop are essentially inmonovalent cation form.
 16. A method as claimed in claim 15,characterized in that the divalent cation is Ca²⁺ and the monovalentcation Na⁺.
 17. A method as claimed in claim 2, characterized in that asequence comprises 4 to 10 steps.
 18. A method as claimed in claim 17,characterized in that a sequence comprising the above steps is repeatedsix to eight times to equilibrate the system, and the process iscontinued in the obtained state of equilibrium.
 19. A method as claimedin claim 1, characterized in that the solution to be fractionated isvinasse.
 20. A method as claimed in claim 19, characterized in that theproduct fractions are a sugar fraction and/or betaine fraction and/orinositol fraction and/or glycerol fraction and/or residue fraction. 21.A method as claimed in claim 19 or 20, characterized in that thesectional packing material beds in the first loop in a process step areessentially in monovalent cation form and the sectional packing materialbeds in the last loop are essentially in divalent cation form.
 22. Amethod as claimed in claim 21, characterized in that the monovalentcation is K⁺ and the divalent cation Ca²⁺.
 23. A method as claimed inclaim 1, characterized in that a system comprising 2 to 12chromatographic sectional packing material beds is employed.
 24. Amethod as claimed in claim 1, characterized in that a sectional packingmaterial bed comprises one column.
 25. A method as claimed in claim 1,characterized in that a column comprises two or more sectional packingmaterial beds.
 26. A method as claimed in claim 1, characterized in thatthe packing material forming a sectional packing material bed is astrong acid cation exchange resin.
 27. A method as claimed in claim 1,characterized in that the temperature of the feed solution and eluentwater is 40° to 100° C.
 28. A method as claimed in claim 1,characterized in that the feed solution has a dry solids content of 35to 65% by weight.
 29. A method as claimed in claim 1, characterized inthat the linear flow rate of the liquid is 0.5 to 20 m/h.
 30. A methodas claimed in claim 1, characterized in that the solution is passedthrough a filtration unit prior to being passed from a sectional packingmaterial bed to the next sectional packing material bed having adifferent ionic form.
 31. A method as claimed in claim 1, characterizedin that the temperature of the feed solution and eluent water is 50° to85° C.
 32. A method as claimed in claim 1, characterized in that thelinear flow rate of the liquid is 2 to 10 m/h.
 33. A method as claimedin claim 1, characterized in that a system comprising 3 to 6chromatographic sectional packing material beds is employed.